Production of commercially pure mercaptans and disulfides



lijm-m. MM., s. P. CAULEY PRODUCTION OF COMMERCIALLY PURE MERCAPTANS AND DISULFIDES Filed June 19, 1945 *..Ill

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Qms www limiting the flexibility of the primary Patented Dec. 7, `1948 UNITEDY'STATES PATENT OFFICE PRODUCTION 0F COMMERCIALLY PURE i MERCAPTANS AND DISULFIDES Stephen l. Cauley, "Garden Qity, N. Y., assigner p p "to Socony-Vacuumoil Company, Incorporated,

`"a corporation fof New `York i 1 Application .une`19, 1945, Serial No, l00,245

`"Ihe present inventionrelates to the recovery of mercaptans and` disuldes nof commercially pure `grade from alkaline solutions which have been used in thetreatment of hydrocarbons.

p The increasing number of` uses `for mercaptans in the chemical industries has vresulted `in an 1anspreciable demand Lfor these materials "in a relatively pure state. However, present methods of n producing relatively `pure `mercaptans tinvolve `chemical.syntheses and are expensive.`

oil `and regenerated by steamingto remove the mercaptans, as such, or by air blowingitoiconvert the mercaptans to disuldes Whichiare recovered by settling or other means. 4In both cases the recovered sulfur compounds are contaminated. 'I-his contamination is duetothe presence of a comparatively highconcentration of entrained oil in the aqueous treating solution-afterib'eng separated from the oil. Almajor `portion of this oil is recovered lwith either the mercaptan or disuliide material. i

The average concentration of mercaptan for disulde in the totally recovered phase is normally less than 50 per cent; This isdue to thefact that entrained oil in the treating solutionlmay vary between 0.1 per cent to 1.5per cent. by volume, which corresponds to the same general limits of mercaptan removal during regeneration.

Some improvement in purity of mercaptans and disuldes could be obtained bydilution of the fat treating solution with water prior to regeneration. This would result in lowering oi viscosity `and holding power of the^isolution for o the contaminating oil. However, in such a method, it would be necessary to evaporate the same quantity of water` from the mercaptan-fre solution to return it to its original efficiency for o,

mercaptan` removal. This in` effect would be Y :treating operation, and is not desirable.

It is an object of the presentinvention to pro-` vide a method for `removing impurities from o aqueous alkaline treating solutions containing mercaptan-sulfur which. in the conventional or customaryprocedure of solution regeneration, prevent the production of commercially pure aliphatic or aromatic mercaptans or alkyl or aryl disulfides. It is another object of the present invention to provide a method for recovering commercially pure niercaptans or disulfides from alkaline treating solutions Without substantial degradation of the product. It is a furtherobject of the present invention to provide a methodnfor recovering commercially pure mercaptans or di; suliides" from alkaline treating solutions without substantiallimitation of the flexibilityof the normal treating processes orthe normal functions thereof. Other objects and advantages willbecome apparent from the following description taken inconjunction with `the drawing which is a more or less diagrammatic flowsheetl of o one embodiment of `the present invention.

l `In general the novel method comprises extracting inercaptans from hydrocarbons, particularly mineral oil and mineral oil fractions, with an aqueous alkaline solution containing, orfdevoid of substances such as alkali metal salts of isobutyric acid, alkali metal salts of hydroxylated aromatic compounds, such as the cresols, alkanolamines and the like well known to the art, which increase the solubility of mercaptansin, or increase the solvating power of, aqueous alka7 liner solutions. Such aqueous alkaline solutions contain substantially the same amount of en; trained sulfur-free hydrocarbonoil as mercapg tans and the hydrocarbons are of substantially the same boiling point as the mercaptans. Thus,

analkaline treating solution containing C1 to Cir niercaptans will contain Cr to`Cv hydrocarbons having a boiling range so close` to that of the corresponding' mercaptans` that separation by fractional distillation is impracticable. `The hydrocarbons "and mercaptans can be separated from the alkaline solution but the resulting mixture of` mercaptans andhydrocarbons doesnot even approximate a commercially pure mercaptan mixture.

In the prior art methods of removing mercaptan sulfur `from hydrocarbon mixtures the aqueous alkaline solution, fouled by the presence of the extracted mercaptans, is regenerated for further use as an extracting solution eitheriby steaming to removethe mercaptans and hydro-` carbons or by oxidation of the mercaptans'to disulildes followed by the removal of the disuldes and the `contaminating hydrocarbons. i. 1

The present invention, on the other hand, provides for contacting the foul alkaline solution with a hydrocarbon or mixture of hydrocarbons which boils at a lower temperature than that oi the lowest boiling mercaptan or disulfide to be obtained in the pure state. The ,foul alkaline solution is contacted with the :aforesaid hydrocarbon or mixture of hydrocarbons prior to regeneration of the alkaline solution and in suiiicient amount to materially reduce the concentration oi original hydrocarbon impurities yinfthe alkaline solution. This step is not to be confused with the prior art practice .of washing-alkaline solutions, particularly those regenerated by 'oxidation, after regeneration to remove disull'ides and/or elementary sulfur to yprevent contamination of the material to be subsequently treated by extraction oi the disulfides and/or elementary sulfur from the regenerated alkaline solution. .Such Washing has not beendorre prior to regeneration but has been done after regeneration. Furthermore, in the prior art practice of Washing the .alkaline solution. after regeneration the :hydrocarbon washing liquid has been chosen .at random solely on the basis of its solvent power for elementary sulfur or disulfides and not espe .cially selected on the basis of the relative .boiling range vof `the hydrocarbon washing liquid and the `:boiling range of the mercaptans and/ or disulfides contained in the regenerated alkaline solution.

After contacting the alkaline solution with the liquid hydrocarbon, the mixture may be steamed `or the hydrocarbons and mercaptans or'disuldes rseparated vin any suitable manner. The mixture of added hydrocarbon, extracted `hydrocarbons .and mercaptans or disuldes vis then `fractionated .to provide an overhead of added hydrocarbon and a residue of mercaptan or disulfide and that portion of the extracted hydrocarbon which has not L remained dissolved in the alkaline solution. In .other words, the solubility of hydrocarbons inthe customary, conventional alkaline treating solu- :tions is .substantially the same regardless of boiling point. Consequently, the .concentration of .original oil in the mercaptans or disuldes recovered as `an .overhead vis reduced. This can be more readily understood by a numerical illustration. v

Thus, aqueous alkaline treating solutions nor- `mally used for the removal of mercaptans from gasoline .contain from about 0.1 per cent to about 1.5 .per cent by volume of the oil being treated and from .about 0.05 per cent to about'1.5 per cent by weight of .-mercaptide sulfur, after separation .from the gasoline following contact therewith. These values Vary because of diierences in the -types of treating solutions used, mercaptan con* *tent -ofthe gasolines treated and other operating variables.

VTo illustrate 4the practical application of the present invention by means of a numerical example of conditions often encountered in mercaptan'removal operations, let it beassumedthat l bonshaving from four to twelve carbon atoms in the molecule, that the mercaptans present in the gasoline to be treated have from one to seven carbon atoms per molecule, and that the total mercaptide sulfur concentration of the fat treating solution to be reduced by regeneration 'is 0.1.

4 per cent by weight or approximately 0.25 per cent by volume of mercaptans.

In order to produce a mercaptan or disulfide oil of commercially chemically pure grade, i. e. 95 per cent mercaptans or disuldes or better as a by-product of regeneration, the concentration of original hydrocarbons or loil in the aqueous treating solution must be reduced prior to regeneration to less than 0.013 per cent by volume by means of dilution with the washing liquid. The treating :solutionis therefore contacted with about 10 per `cent byvolu'me of hydrocarbon Washing material in a separate system before regeneration to obtain substantially l.complete equilibrium. After .the -mixture of hydrocarbon Washing material and Ystill contains 0.25 per cent by volume mercaptans and a total of approximately 0.3 per centiby volume of hydrocarbons. A portion of these hydrocarbons are those derived from the hydrocarbon Washing material and the remainder are the hydrocarbons originally present in the unregenerated aqueoustreating solution. The 0.3 `per centby volume of hydrocarbons in the washed aqueous treating solution is composed of 0.009 per cent by 'volume of hydrocarbons originally present inthe aqueous treating solution before Washing with the hydrocarbon washing material and 0.291 per cent by volume of hydrocarbons 'from 'the hydrocarbonV Washing material. In other words, the `washed aqueous `creating solution lbefore regeneration vwill retain substantially 'all ,ofthe mercaptides originally present as they have a chemical bond with the solution and about `0L3 `per cent by volume v`of the Vvhydrocarbons derived partially from those `originally present in v'the aqueous unregenera'ted Atreating solution and Apartially Afromthe hydrocarbon washing material. '.The'ihydrocarbons of the mixture are composed of`100r(0;3/10.3)=2.91 per cent-by volume of the original 'hydrocarbons 'and 100 (10/10.3)=97.09 percent :by volume'of hydrocarbons of the washing "materiaL Therefore,` the 'aqueous Washing material will contain 502911 0.`3 -.009per cent by `volume .original 'I hydrocarbons :and .9709X 0.3: .'291 per cent 'by 4'volume hydrocarbons -of the vWashing.material f "-Ihe Pwashed'.faqueous .treating `solution may 4.then besteamed in va `conventional manner of solution regeneration to recoveranoverhead com- -prisingthydrocarbons from vthe washing material, thefresidual :originalhydrocarbons fand the mer- The overhead can .'abefractionated into two cuts: the'zrstccut comprising the hydrocarbons from lthelwashing materialand the second cut com- .polsed ,-otfcommercially pure `mercaptans having a purity of "Per @entryl n. PL, r. 76o mfn Hg volume i ;1 ABS C Propanenl...`-;...;... `52.91 44. Mercaptans w45. 45 43 to 420. Original hydrocarbons.; 1.64 to approximately 420.

This materiallcan be fractionated readily tore;- move all the propaneleaving a` mercaptan oil `of approximately 96.5per cent purity. t i .t

, When disuliides areto be recovered, the washed solutioncontaining'areduced amount of the hydrocarbons originally` `present is regeneratedby oxidation and the `disulides 'being `insoluble are recovered bymeans of settling or any other;-:.uit` able method. The degree of purity of thetrecovered disuldes is the `saine as that of the mercaptana]` i. l" The washing liquid in allfcases `may be returned to the reiinery fractionation "equipment fior recovery." When disuliides ar"e"t`o be recovered the washing liquid may be added directly to the treated gasoline or other petroleum fraction;

The foregoing discussion` illustrates thebroad concept that the `hydrocarbon washing material is selected on the basis of the boiling point of the most volatile mercaptan present inthe unregenerated aqueous treating solution or upon the boilingpoint of the most volatile disulfide which lwill be produced byoxidizing during regenerationgthe mercaptans originally present `in the aqueous treating solution. `Thus when the mercaptan to be" obtained in relatively pure state, i. e. commercially pure, is` a mixture of butyl mercaptans containing t-butylmercaptan which has a `boiling point at atmospheric pressure of about`149 F., the hydrocarbon lwashing liquid may have a iinal boilingl point of approximately 140 On th'e` otherhand, if itisproposedtorecover disuldes of commercial purity in which disuliides to be recovered after regeneration by oxidation dimethyl disuliide is present, other hydrocarbon washingimaterials may be employed to Washlthe unregenerated aqueous treatingsolution. This hydrocarbon` washing liquid may belselected on thebasis `ofthe boiling point of dimethyldisulfide Whichhas a boiling pointof 240.8 F. Under these circumstances the hydrocarbon washing material may have a final boiling point of` approximately 230 F. Similarly, when theinitial mercaptan tobe obtained in relatively pure state, i.v e. commercially pure,` is a mixture of butyl` mercaptanscontaining t-butyl mercaptanuhaving a boiling point atatrnospheric pressure ofabout` 149 F., the hydrocarbon washing liquid may` have a iinal boiling point of approximately 140i F `In general, the differential in boiling point between the endpoint ofthe hydrocarbon washing ma terial and theimost volatile'mercaptan or disulfide is `about 10` degrees toabout215pdegrees Fahrenheit. `'llhat is, when precise highly eilcient fractionating equipment is used a differential of `10 degreesFahrenheit provides satisfactory .ref

su1ts. `On the` other hand, when present 1 day industrial fractionating.,equipment is used a differential of about 45degrees to about 215 degrees Fahrenheit` isnecessary `to obtain a; satisfactory separation. v .i l In order that those skilled in the `art may readily visualize the` sequenceof` operations: `of one `embodiment of thegpresentinvention, the more or less diagrammatic owsheetof the drawing has been provided. `Those skilled in the4 arti will. recognize that the principles oflthe present inven' tionoan be applied to thetreatment of any aquef ous alkali treating `solution containngmercapftides and hydrocarbon impurities of` substantially the samwboiling point asthe contained mercaptans` and that under such` circumstances the process of the present invention does notlinvolve the steps necessary `to obtain the; fouled or `fat aqueous treatinglsolutionw l, 1 ,z r. inthe usual or `conventional process for rel moving mercaptans` andthe; like from petroleum fractions such `as` gasoline, the extraction tower l is filled with aqueous alkali metal hydroxide soi lutioncontainingsolutizersor devoid of solutizers.

Rawgasoline lcontainingMniercaptans is introduced intortower i atta *point 2 below themid point of the `tower but suiilcientlyabove-:lthe bottomllthereof that no materialamount :ofllth petroleum fraction is 4carried `out fof. the 1 tower with `theiouled or fat aqueous solutionwcontain ing` the `dissolved mercaptan's. fIhe fataqueoiis i solution leaves thetower at 3. wilh'eirawpetroleum may be of any'suitabletype` to provide intimatev fraction, `for example, gasoline `rises in the Vtower and is` withdrawn at 4. f `In l a i continuous operation regenerated or lean aqueous alkali metal h5"'d1ox` ide solutionisyintroduced into tower `I at 5`fby means.` of sprays l 6; In order ito maintain proper operationalfbalance a valve l isplaced in' linef throughpwhichthe fouled or fat `aqueous solution is Withdrawnifrom the `bottomof tower fl. l Valve 'itiscontrolled by the conventionalliquid level control 9 whereby `valve "i1 `is 1 opened and: closed to maintain the upper level of theaqueoustreat-` ing solution approximatelyas indicated by" dotted linel. i l i' l i i i C i .The fat oriouled aqueous treatinglsolution is withdrawn` through linew and "at Il` hydrocarbon washing` material .u such `as propane1 or the like as indicated hereinbefore is introducedlf` Theimixture of `hydrocarbon washing material `andiat aqueous solution `passes l, to.` contactors II 2 which contact between the `fat `'treating .solution andthe hydrocarbon ,washing material 1 :l and tol `permit reaching `an `equilibrium between thehydrocar-bon washing liquid` and the fat aqueous `treating solu# tion. `After a state of substantial "equilibrium is reached inoontactorsil! the mixture ofwashing liquid l and u aqueous treating` solution is passed through conduit-i3 to` settlerii where thewashl ing liquid isi withdrawn `through :pipe i 5 and either introduced into pipe I6 throughxwhich thetreate'd i fraction isawithdrawnfrom tower `I or passed directly tothe reiirlery` through conduit` |`1.` The foregoing choice `is controlled by valves I 8 and I9 anddictatedv by ithevcomposition of the liquid withdrawnthrough15.` 1w ii" The washed" fatr "aqueous "treating, solution is withdrawn?. from the settler` I4 -by line 20E The' washed fat aqueous solution then passes either through `line 2i" controlled `by valve `22mto heater 23 forseparationvoi mercaptans' by steaming or,` through `line `24 controlled by valve"25` to=coni tactors 26 `whereinthe mercaptans are oxidized to disulfides `by oxidizingtgas such l as oxygen,' air benzene carboxylic` acidi and esters, derivatives Aand condensation products thereof.

The washed aqueous treating 'solution after oxidation of the mercaptansito disuldesin contactors l 28 is then transferred to a settling tank 2flinlany suitable manner-asbfy line V28. Excess oxidizing gas.` is withdrawni'rom settler 21u/hen necessary by'means o1' conduit 29. The commercially .pure disuld'es are YWithdrawn from settler'-Tk inanyfsuit'able manner as by overflow pipe .30. vtiter separation `of vthe commercially pure:disulfides the regenerated aqueous f treating solution .is Withdrawn `from settler 21 'through pipe 3| by pump 32 and' returned totower l by linesf 133 and' 34. 'Of course', 'thef regenerated solution can bewithdrawn from settler 21 and returned to ltower l in any other suitable manner. When it is desirable or necessary to recover iliesrnelfcapt'ansrasf.` commerclally'pure mercaptans rather than as dsul'des, the 'fatorioul aqueous treating solution .iswithd'rawn Afrom settler -li4 aitcrzthe. removal of `excess hydrocarbon Washing liquid, and ipassedinto Vheater 23. In heater 23 the temperature: ofthefat aqueous treating solution.' isxraisedto about220v to about1 270 degrees Fahrenheit.. `.'llhe heatedy 'aqueous solution 'is Withdrawn from heater-i23'through line 35 under control .of flow recorder control device 36 of customaryv and conventlonaldesign to regenen ato: 31.

In regenerator Slitherheated aqueous solution containing .mercaptans "and impurities in com; merci'al-ly acceptable quantities are Vaporized by the heat introduced bymeanso'iV steam coil 38 having inlet-.3:9 andoutletl'. `Asfis usual practice in regeneration by steamingl anoverhead of mercaptans, impurities `and 'water *is taken off at 4|. However, it must beemphasized that Whereas: in conventional steaming regeneration the mercaptans contain about 50 per cent commercially' inseparable impurities, the present overhead contains' alniaximum of 10 per cent impurities; and preferably a maximum of 5 per centimpurities..v

The'. overhead .is lpassed to -condenser 42 by any` Asuitable vmeans such as line v43. The condensate: thereofV ows through line 44- to separatord where the mercaptans are separated irom'thezwater of the overhead. When the composition of' 'ther condensate warrants it, water vaporandmr low boiling range mercaptans are withdrawn fromseparator as overhead through pipe 46'.. .The heavier mercaptans -areWithdrawn througlran .overflow pipe Hand ycondensed Water through line 48. Pump 491returns'the aqueous condensate irom'separator` `45'fthrough line 50 to regeneratorlfaslreilux. l y

.Inl AView of the foregoing description, those skilledlin :the Vart 'will understand that' the present novely methodA of recovering mercaptans and/orl disuldes from aqueousv `treating solution containing mercaptans contaminated'with impurities :boiling'withinthe boiling range of the mercaptans-and present. .in commercially unacceptablel amounts; comprisesl vcontacting the fat aqueous treating solution prior to regeneration thereof with hydrocarbon material' having a. boiling range' suiciently lower .than the .boilingy point of the,V most `volatile mercaptan or disul'def :to herecovered that; thexhxdrocarboni'material! can 8 be `readily `separatedl bydistillation `and thereafter recovering the mercaptans rand/'or "disuld'es.

It will also bey understood by those skilled in the art that when it is desirable ornecessary to recover the -mercaptans 'in the form `of their disuldes the mercaptans are oxidized to disuld'es after the aqueous treatingsolutlon has been treated with thehydrocarbon material having aboiling range vhelowthat .of the most volatile disulde to be recovered. 1 f Y It Will be understood that when the hydrocarbon. treating material is not volatile at ambient temperatures and atmospheric pressure the hydrocarbon treating material is recovered with the mercaptans and/jor disuldes and then-separated by a simple fractionation.

I claim:

1. The method of treating aqueous alkaline solutions to obtain commercial-ly pure Hsulfur compounds which alkaline solutions have been used to extract acidic` sulfur compoundsl from hydrocarbon fluids and which containhydrocarbon impurities of substantially thesame boiling range as said acidic sulfur compounds in 'commercially unacceptable amounts which comprises contacting said aqueous solution before regeneration with hydrocarbon treatingmaterialhavinga boiling range differential of `at least 10 -degrees from that of the sulfurbearing compound to'be recovered and separating said hydrocarbon treating material and said sulfur compound from said aqueous treating solution.

2. The method of treating aqueous alkaline solutions to obtain commercially pure sulfur compounds which alkaline solutions have'been used to extract acidic sulfurcompound's fromhydroycarbon liquids and Awhich solutions contain hydrocarbon impuritiesof substantially the same boiling range asA said acidic sulfur compounds in commercially unacceptable amounts which comprises contracting such aqueous solution'before regeneration with a hydrocarbon 'treating materialhavingaboiling range end' point about 10? F. to about '215 F; below that of' the boiling point ofthe most volatile sulfur bearing compound to be recovered, separating said' hydrocarbontreat.- ing-material and said sulfur compound from' said aqueous treating solution, and separating said sulfur bearing compound fromsaidhydrocarbon treating material by distillation. A

3. The method of treating aqueous alkaline solutionsv to obtain commercially pure. sulfurcomfpounds which alkaline solutions have been ,used to extract acidic sulfur compounds from hydrocarbon ulds and which solutions contain. hydro.- carbon impurties'of substantially the same boil'- ing range as said acidic sulfur compounds in commercially'unacceptable amounts which com-- prises contacting saidI aqueous solution before. re.- generation with a hydrocarbon treating .material having a 4boiling range end point at least'l'O F; lower than the boiling point of the most" volatile sulfur compound to be recovered, the Avolume o! said hydrocarbon treating material Vbeing such that whenequli-britun is reached .the concentration of the aforesaid impurities will be'reduced' to predetermined amounts, separating'sulfur compounds from said aqueous treating solution, said hydrocarbon treating materialv and commercially unacceptable amounts Aof hydrocarbon impurities, and separating sulfur compounds from 4hydrocarbon treating material by distillation.

4.- The methodof treating aqueous Aalkaline solutions to'obtai'n cormnercially pure-sulfur commaterial being' such .as to...reduce the .concentraf tionv of` impurities to predeterminedamounts at' equilibrium, separating the, bulk .of' said'. hydro? carbon treating.` materiallfrom said, fat, aqueous treating` solution,4 andi. oxidizing said.. mercaptans. in saidfat aqueoustreatingsoluti'on todisuldes in the presence of' an organic, oxidation. prof, moter selected from the.groupconsisting;oflpoly hydroxy aromatic compounds, polyhydroxy ben.- z'e'ne carboxylic acids and`.esters-, derivatives and condensation productsfof said acids.v y

11..In.the methodof reactivatingfaqueous al-A kalf. solution. which. has beenv usedto extract weakly, acidic. sulfur compounds.V from. hydrocarbon fluids to obtain..areactivated alkalisolution andi a. mixture of..` one-of ther organic sulfur oom.- pound's. selectedl fromv the. group consisting of mercaptans. and4 disuldes. with hydrocarbons` ot, substantially the sameboiling range. as,` said! organic. sulfur compounds in commercially unac.`

ceptable amounts the improvement. which.

comprises contacting. said", alkali solution. .before reactivation. with .hydrocarbon treating;,material= having. a boiling. range. diiierenti'al'Y of. atleast about' 10 degrees. Fahrenheitrffrom. that of. the most' .Volatile -sulffur compounito be. recoveredreplace a,y portion. of. said( hydrocarbon imiznuritiesi by said. Lhydrocarbon .treating` material..

12'.. Inthemethod of. reactivating aqueous -alkali., solution. which. has been used to..V extract;

t2 weakly acidic .sulfur clompoundsvlfrom.v hydrocai', bon uidsto. obtain a. reactivatedalka1i solution and a mixture of. one ofthe organic sulfurL com: pounds selectedv from the.group consistingof mercapt'ans anddisuldes with hydrocarbons of substantially the same boiling; range as saidorganic sulfur compounds in commercially unacceptable amounts, the improvement which comprises contacting. said. alkalilsolution. before reactivation with hydrocarbon.. treating mat'eti'al havingV a boiling range differential. of'v at" least about 45LdegreesFahrenheit to about 215', degrees Fahrenheit from. that of the most Volatilesullur compound to be .recoveredto replace aporti'onof said hydrocarbon` impuritiesby said hydrof carbon treating material;

' STEPHEN P; CAULEY.v

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